Inkjet printheads typically expel ink through very small nozzles on the printhead. In thermal inkjet printheads the ink is moved by vaporizing water or other component of the ink employing a semiconductor substrate (chip) having resistors proximate to each nozzle. The nozzles are very small and may become clogged.
To minimize clogging, prior art inkjet printheads contain a filter between the main reservoir for ink and the channel to the chip. Such filters are of a fine mesh which prevents any potentially-clogging contaminants from passing through the filter. In order to anchor the filter, each reservoir has a standpipe leading to its flow channel to the chip. The standpipe presents a round regular top to which the filter can be fixed by heat staking or other process. Also, inkjet printheads in the prior art are made in isolated, decontaminated "clean" rooms, such as those used for semiconductor manufacture.
It has been found in accordance with this invention that the foregoing standpipe and filter, and clean room manufacture, are only partly effective in eliminating clogging of nozzles from contamination. It is the premise of this invention that regions between the top of the standpipe and the end of channels to the chip are sources of contamination because they are functionally past the filter.